THE ULTRASTRUCTURAL DEVELOPMENT OF THE MACROGAMETE AND FORMATION OF THE OOCYST WALL OF TOXOPLASMA GONDII

Abstract

Siim, J. Chr. The ultrastructural development of the macrogamete and formation of the oocyst wall of Toxoplasnia gondii. Acta path. microbiol.scand. Sect. B, 83: [491][492][493][494][495][496][497][498][499][500][501][502][503][504][505] 1975.The macrogametes of Toxoplmrna gondii develop within the epithelial cells of the cat ileum. As they develop the nucleus enlarges and dense patches of chromatin which were present in the nucleoplasm, disappear. Polysaccharide granules and lipid globules appear in the cytoplasm and increase in number during development. The wall-forming bodies of Type I (WFB I ) appear before the wall-forming bodies of Type I1 (WFB 11) ; WFB I are smaller, more osmiophilic and more numerous than the WFB 11. The WFB I appear to form from vesicles produced by the smooth endoplasmic reticulum, and the WFB I1 form within the lacunae of the rough endoplasmic reticulum. Double membraned vacuoles appear to form from the nuclear membranes but the function of these is unknown. Throughout development the macrogamete retains a normal pellicle which possesses numerous micropores. The first evidence of oocyst wall formation is the appearance of participate matter in the parasitophorous vacuole which precipitates to form Layer 1 of the oocyst wall. Layers 2 and 3 are unit membranes which form between Layer 1 and the pellicle. During this development the organism has an organelle complement similar to that of the macrogamete. Layers 4 and 5 form between 1,ayer 3 and the pellicle. Layer 4 is osmiophilic and its formation is accompanied by the disappearance of W F B I . Layer 5 is less osmiophilic than Layer 4 and its formation is accompanied by the disappearance of WFB 11.The two innermost layers (Layers 4 & 5 ) in the oocyst wall of Toxoplasma are similar to those found in Irospora spp. and Eimeria spp,. Toxoplasma seems to be unusual in that, firstly, it possesses an additional 3 layers and, secondly, all 5 layers are formed outside the pellicle of the original macrogamete.Prior to 1969, only the exo-enteric stages of Toxoplasma gondii were known. These two stages were found in many mammals and birds and are now known as endozoites and cystozoites (Hoare 1972). Both stages repro-

Oocyst wall formation and composition in coccidian parasites

“…The oocyst wall is formed from the contents of two specific organelles, wall forming bodies Type 1 (WFB1) and 2 (WFB2), found exclusively in the sexual, macrogamete stage of coccidian parasites (Scholtyseck et al 1969, Scholtyseck 1973, Ferguson et al 1975, Pittilo & Ball 1980, Belli et al 2006. In the early stages of macrogamete biogenesis, the macrogametocyte contains a centrally-located nucleus and numerous spherical deposits of electron dense material within swollen regions of the rough endoplasmic reticulum; these represent the early WFB2.…”

Mechanics of the Toxoplasma gondii oocyst wall

“…The oocyst is the result of sexual multiplication of T. gondii in the intestinal epithelium of cats (19)(20)(21). A few days postinfection, unsporulated (uninfective) spheroid oocysts (10 × 12 μm) are excreted in cat feces and become rapidly infective following aerobic sporulation (22).…”

MORN1 Has a Conserved Role in Asexual and Sexual Development across the Apicomplexa

“…The motile microgametes are unique within the coccidian life cycle in possessing flagella. In contrast, macrogametogony involves an increase in size, but no nuclear division, and the synthesis of material required for oocyst wall formation (wall-forming bodies) and storage (polysaccharide granules and lipid droplets) to allow the mature macrogamete to develop into the oocyst and undergo sporulation in the external environment (8,12,34). In the present study, while examining the asexual development in the definitive host, we also examined the expression of MORN1 during sexual development in T. gondii and in the three species of Eimeria.…”